Kinetic compensation effect in depolymerisation of food polysaccharides

The thermal depolymerisation kinetics of agarose and kappa-carrageenan in water were investigated by measurement of intrinsic viscosity ([eta]) An isokinetic relationship (IKR) revealing a kinetic compensation effect in polysaccharide depolymerisation was then discovered from the obtained kinetic data and those reported in the literature. Generally, the Arrhenius frequency factor, k(0), and activation energy, E-a, of depolymerisation of agarose, kappa/lambda-carrageenan, kappa-carrageenan and schizophyllan, under commonly used thermal conditions (high temperature, in water or pH-7 solvents, without deaeration and in disordered conformation), were in the ranges of 1.8x10(7)-7.8x10(10) s(-1) and 97-126 kJ mol(-1), respectively. These two variables showed parallel increases when using solvents of lower pH values (especially in k(0)) or with deaeration, and polysaccharides in ordered conformation or at lower concentrations. The IKR for the polysaccharide depolymerisation was: In k(0)/s(-1) = 0.379.E-a/kJ mol(-1)-18.5 (R-2=0.906), giving an isokinetic temperature (T-iso) of 317 K. Conclusively, the depolymerisation mechanism was the same for all polysaccharide systems examined. (C) 1999 Elsevier Science Ltd. All rights reserved.